Our proposed research is multiphasic and includes: The effect of artifical cardiac pacing on control of bradycardias and tachycardias; the clinical course of paced patients, including underlying rhythm, morbidity, mortality and the functional reliability and utility of existent pacing equipment; development of new equipment of improved flexibility, utility, reliability and longevity toward the "ideal pacemaker"; the utility of electronic "clinic" and transtelephone monitoring; computer record keeping, retrieval and analysis system for the massive clinical, electronic and physiologic data we develop; definition of causes of malfunction, electrical, electronic magnetic, unusual intracardiac currents; analysis of the intracardiac electrograms and their influence on pacemaker triggering; development of non-invasive techniques of measuring pacemaker function and cardiac response; the influence of drugs on threshold to pace, cardiac output and intracardiac voltages. Our objectives are: 1) To make pacemakers flexible, reliable, long lasting; 2) To prolong life in as near physiologic function as possible; 3) To understand better the interrelationship of pacing and the patient; 4) To set standards of safety and performance. This year we will expand statistical analysis of computerized data seeking trends and correlations; further pursue His bundle studies for prognostic as well as diagnostic value; expand techniques of tachyarrythmia analysis and treatment to new drugs, specially designed pacemakers and operative mapping; intensify study of interference, pollution and protection.